Method and structure for an out-of plane compliant micro actuator

ABSTRACT

This present invention relates generally to manufacturing objects. More particularly, the invention relates to a method and structure for fabricating an out-of-plane compliant micro actuator. The compliant actuator has large actuation range in both vertical and horizontal planes without physical contact to the substrate. Due to fringe field actuation, the compliant actuator has no pull-in phenomenon and requires low voltage by a ‘zipping’ movement compared to conventional parallel plate electrostatic actuators. The method and device can be applied to micro actuators as well as other devices, for example, micro-electromechanical sensors, detectors, fluidic, and optical systems.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application claims priority to provisional application Ser. No.60/732,010; filed on Oct. 31, 2005; commonly assigned, and of which ishereby incorporated by reference for all purposes.

BACKGROUND OF THE INVENTION

This present invention relates generally to manufacturing objects. Moreparticularly, the invention relates to a method and structure forfabricating an out-of-plane compliant micro actuator. The method anddevice can be applied to micro actuators as well as other devices, forexample, micro-electromechanical sensors, detectors, fluidic, andoptical systems.

Micro Electro Mechanical Systems (MEMS) is a rapidly emerging technologycombining electrical, electronic, mechanical, optical, material,chemical, and fluids engineering disciplines. A common MEMS actuator isthe electrostatic comb drive which consists of rows of interlockingteeth; half of the teeth are attached to a fixed “beam”, the other halfattach to a movable compliant beam assembly. Both assemblies areelectrically insulated. By applying an opposite polarity voltage to bothparts the resultant electrostatic force attracts the movable compliantbeam towards the fixed.

As merely an example, some conventional MEMS actuators have utilizedvarious comb drives designs, such as the movable compliant beam isin-plane with the fixed beam. In some of these designs, the movablecompliant beam are out of plane relative to the fixed beam and rotatesin and out of the fixed beam. However, in these designs, comb drives arerigid structures and have short actuation range or stroke. Thus, thereis a need in the art for methods and apparatus for fabricating anout-of-plane compliant micro actuator with large actuation range.

SUMMARY OF THE INVENTION

According to the present invention, techniques for manufacturing objectsare provided. More particularly, the invention provides a method anddevice for fabricating an out-of-plane compliant micro actuator. Themethod and device can be applied to micro actuators as well as otherdevices, for example, micro-electromechanical sensors, detectors,fluidic, and optical systems.

According to a specific embodiment of the present invention, a structureof an out-of-plane compliant micro actuator is provided. The structureincludes a substrate member and a movable compliant actuator memberanchored at one end to the substrate. The movable compliant actuatormember is a stressed film or a stack of films with different Coefficientof Thermal Expansion (CTE). The neutral position of the movablecompliant actuator is a curvature where the internal stress of the filmbalances a mechanical spring force of the curved film.

A plurality of openings are spatially disposed along the movablecompliant actuator. The openings overlap a plurality of fixed electrodemembers on the substrate. A voltage potential applied between theelectrodes and the movable compliant actuator creates fringe electricalfield between the opening edges and electrode edges. The fringeelectrical field results in an electrostatic force that attracts themovable compliant actuator member to the fixed electrodes. The openingsare larger than the electrodes and encircle the electrodes withoutcontact when the curved movable compliant member flattens by theelectrostatic force.

According to another embodiment of the present invention, the substrateis a silicon wafer with Integrated Circuits (IC). The IC drives themovement of the actuator and controls the position of the actuator.According to an alternative embodiment of the present invention, thesubstrate is a glass with Thin Film Transistors (TFT). The TFT drivesthe movement of the actuator and controls the position of the actuator.

Many benefits are achieved by way of the present invention overconventional techniques. For example, the present technique provides aneasy to use process that relies upon conventional technology. In someembodiments, the method provides for a micro actuator with largeactuation range or stroke in both vertical and horizontal planes. Inother embodiments, the method provides for a micro actuator withoutphysical contact to any other members of the substrate. The non-contactnature of the actuation avoids common stiction and wear in MEMS devicesthat surfer long-term reliability issues. Furthermore, the fringe fieldactuation has no pull-in phenomenon associated with conventionalelectrostatic actuation. In other embodiments, the ‘zipping’ actuationof the movable compliant member requires low voltage compared toconventional parallel plate electrostatic actuators.

Additionally, the method provides a process that is compatible withconventional process technology without substantial modifications toconventional equipment and processes. Preferably, the invention providesfor an improved integrated structure including integrated circuits andout-of-plane compliant micro actuator for various applications.Depending upon the embodiment, one or more of these benefits may beachieved. These and other benefits will be described in more throughoutthe present specification and more particularly below.

Various additional objects, features and advantages of the presentinvention can be more fully appreciated with reference to the detaileddescription and accompanying drawings that follow.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a perspective view of an out-of-plane mechanical structure ora flap according to one embodiment of the present invention.

FIG. 1B is a simplified side-view illustration of the out-of-plane flapaccording to one embodiment of the present invention.

FIG. 2A is simplified side-view illustration of the out-of-plane flapstructure in an “up” position or neutral position according to oneembodiment of the present invention.

FIG. 2B is simplified side-view illustration of the out-of-plane flapstructure in an intermediate position according to one embodiment of thepresent invention.

FIG. 2C is simplified side-view illustration of the out-of-plane flapstructure in a “down” position according to one embodiment of thepresent invention.

FIG. 3A is simplified top-view illustration of opposite comb fingers areinterlaced with each other in an “up” or neutral position according toone embodiment of the present invention.

FIG. 3B is simplified top-view illustration of opposite comb fingers areinterlaced with each other in a “down” position according to oneembodiment of the present invention.

FIG. 4 is simplified diagrams illustrating components and operation ofan out-of-plane compliant comb drive device according to one embodimentof the present invention.

FIG. 5 is simplified diagrams illustrating components and operation ofan out-of-plane compliant comb drive device according to one embodimentof the present invention.

FIG. 6 is simplified diagrams illustrating components and operation ofan out-of-plane compliant comb drive device according to one embodimentof the present invention.

FIG. 7 is a simplified perspective view of an out-of-plane compliantactuator device according to one embodiment of the present invention.

FIG. 8 is simplified diagrams illustrating components and operation ofan out-of-plane compliant actuator device according to one embodiment ofthe present invention.

DETAILED DESCRIPTION OF THE INVENTION

According to the present invention, techniques for manufacturing objectsare provided. More particularly, the invention provides a method anddevice for fabricating an out-of-plane compliant micro actuator. Themethod and device can be applied to micro actuators as well as otherdevices, for example, micro-electromechanical sensors, detectors,fluidic, and optical systems.

FIG. 1A is a simplified 3-D diagram illustrating components of anout-of-plane mechanical structure or a flap according to one embodimentof the present invention. As shown, the out-of-plane mechanicalstructure 103 is coupled to a substrate 101 at the one end by an anchor105. According to one embodiment of the present invention, the movablecompliant actuator member is composed of a stressed film such asAluminum, Titanium, TiN, Copper, amorphous Silicon, poly Silicon, singlecrystal Silicon, SiO2, Si3N4, or metal alloy. According to anotherembodiment of the present invention, the movable compliant actuator is astack of films with different Coefficient of Thermal Expansion (CTE)such as Aluminum/Ti, Aluminum/TiN, TiN/amorphous Silicon. The neutralposition of the movable compliant actuator is a curvature where theinternal stress of the film balances a mechanical spring force of thecurved film. FIG. 1B is a simplified side view of the out-of-planemechanical structure.

FIG. 2 is simplified side diagrams illustrating components of anout-of-plane compliant comb drive device according to one embodiment ofthe present invention. As depicted in FIG. 2A, the “up” position 201 isthe neutral position of the curved flap structures or comb fingers 202.When a voltage potential 203 is applied between the two comb finger orelectrodes as shown in FIG. 2B, the comb fingers are attracted to eachother to an intermediate position 207 by an electrostatic force inducedby fringe fields 205 between the comb finger electrodes. The combfingers eventually reach a final flat position 209 where theelectrostatic forces balances the mechanical restoring force of thestressed film as illustrated in FIG. 2C.

FIG. 3 is simplified top view diagrams illustrating components of anout-of-plane compliant comb drive device according to one embodiment ofthe present invention. As depicted in FIG. 3A, the opposite comb fingers202 are interlaced with each other, however, without contact. In the“up” position, the comb fingers are curved and have little over lapportion to each other from the top view 301. When a voltage potential203 is applied between the opposite comb fingers, they attracted to eachother by an electrostatic force induced by fringe fields between thecomb fingers and reach a final flat position 303 where the electrostaticforces balances the mechanical restoring force of the stressed film asillustrated in FIG. 3B.

FIG. 4 is simplified diagrams illustrating components and operation ofan out-of-plane compliant comb drive device according to one embodimentof the present invention. As depicted in the top-view diagram, the combon the left 401 is flexible or movable compliant, where as the one onthe right 403 is fixed. When no voltage potential is applied between thetwo combs, the flexible comb is in an “up” or neutral position 405. Whena voltage potential 407 is applied between the two combs, the movablecompliant comb structure is attracted to the fixed comb structure to anintermediate position 411 by an electrostatic force induced by fringefields between the comb fingers. The movable compliant comb eventuallyreach a final flat position 412 parallel to the fixed electrodes asillustrated in the side and top view diagrams.

FIG. 5 is simplified diagrams illustrating components and operation ofan out-of-plane compliant comb drive device according to one embodimentof the present invention. As depicted in the side and top view diagrams,the flexible or movable compliant structure has two portions: aperforated comb portion 501 that is close to the anchor and a continuousportion 503. The comb portion has a matching fixed comb 505. When avoltage potential is applied, the comb portion is attracted to the fixedcomb by fringe field similar to actuation mechanism described above. Thetwo continuous portions of opposite side face each other and areattracted to each other largely by a direct electric field 507.

As the curved movable compliant structures become fatter, the facingarea become smaller, which results in a smaller direct electric field,and the fringe field 601 between the edges becomes dominating attractingforce. At the final flat position 603 , the two actuators are attractedto each other largely by a fringe electric field as illustrated in FIG.6.

FIG. 7 is a simplified 3-D diagram illustrating components of anout-of-plane compliant actuator device according to one embodiment ofthe present invention. As depicted, the curved structure 701 has aplurality of cut-outs or openings 703 parallel to the anchor 705. Theopenings overlap with the fixed electrodes 707 on the substrate to forma pair of electrodes.

FIG. 8 is simplified diagrams illustrating components and operation ofan out-of-plane compliant actuator device according to one embodiment ofthe present invention. As depicted in the side view diagrams, themovable compliant electrode 801 is attracted to the fixed electrodes 805by fringe fields when a voltage potential 807 is applied between them.The movable compliant electrode eventually reach a final flat positionparallel to the fixed discrete electrodes as illustrated in the side andtop view diagrams.

It is also understood that the examples and embodiments described hereinare for illustrative purposes only and that various modifications orchanges in light thereof will be suggested to persons skilled in the artand are to be included within the spirit and purview of this applicationand scope of the appended claims.

1. An actuator device, the actuator device comprising: a substratemember, the substrate member comprising a surface region; a movablecompliant actuator member having a fixed end, a free end, and a lengthformed between the fixed end and the free end, the fixed end beingcoupled to a portion of the surface region, the actuator member havingat least a first state at a first spatial position and a second state ata second spatial position, the free end being at the first spatialposition during the first state, the first spatial position being afirst predetermined height normal to the surface region and the secondspatial position being a second predetermined height normal to thesurface region; an arc region defining a path between the first spatialposition and the second spatial position, the actuator member being in astressed state at the second spatial position, the stressed state beingin a direction toward the first spatial position; a plurality ofelectrode members spatially disposed along a first region of the surfaceregion and a second region of the surface region, the first region beingwithin a vicinity of the portion of the surface region coupled to thefixed end of the movable compliant actuator member; whereupon one ormore of the electrodes is capable of being biased relative to themovable compliant actuator to cause the movable compliant actuatormember to move along the arc region from the first spatial position tothe second spatial position; and wherein the actuator member comprises aplurality of openings therein, the plurality of openings being providedto form a pair of electrodes with the plurality of fixed electrodewithin the surface region.
 2. The device of claim 1 wherein each of theelectrodes is actuated to cause the movable compliant actuator member tobe in the second spatial position.
 3. The device of claim 1 wherein theactuator member, except for the fixed end, is free from physical contactwith the surface region.
 4. The device of claim 1 wherein each of theplurality of electrode members is characterized by a length and a width,the length being provided in a direction normal to the length of theactuator member.
 5. The device of claim 1 wherein each of the pluralityof electrode members is embedded within the surface region.
 6. Thedevice of claim 1 wherein the substrate comprises a silicon waferincluding one or more integrated circuits.
 7. The device of claim 1wherein the substrate is a TFT glass substrate.
 8. The device of claim 1wherein the movable compliant actuator member is made of a stressed filmselected from: Aluminum, Titanium, TiN, Copper, amorphous Silicon, polySilicon, single crystal Silicon, SiO2, Si3N4, or metal alloy.
 9. Thedevice of claim 1 wherein the movable compliant actuator is a stack offilms the stack of films selected from films of different Coefficient ofThermal Expansion (CTE) including Aluminum/Ti, Aluminum/TiN,TiN/amorphous silicon.